One man's steps to a greener lifestyle.

Monthly Archives: August 2019

The height of summer is perhaps an odd choice of time for a post about heating, however we’ll get to that. Regular readers may recall that our smart heating controls enable the boiler when any radiator demands heat via its smart valve (eTRV) and disables the boiler when the last room is up to temperature. That rather begs the question what happens to the control logic when the batteries go flat. The HomekIt rules are not sufficiently sophisticated for the author to set that behaviour via the program, and I’ve seen no default behaviour described on-line.

Today the inevitable happened and a battery did go so low as to stop operation. The behaviour of the heating was to force the boiler on. Most rooms did not heat up as their own eTRVs recorded them already being sufficiently hot, although the bathrooms and cloakrooms did heat up (they generally lack eTRVs) as indeed did the room with the flat battery (my daughter’s playroom). Other symptoms included an icon in the Home app that would not grey out when disabled like other room eTRVs and the the boiler repeatedly being re-enabled even after manually disabled through the app.

Although any more heat input is unwelcome on a day as hot as today, we have at least demonstrated that the system is failsafe in a flat battery condition – I’d rather that the system heated up with a flat battery to prevent freezing damage in winter at the cost of some discomfort in summer due to excess heat.

It’s 265 days since my records indicate an earlier battery change, albeit for most of that time the heating hasn’t been on (so no power needed for valve movements). It’s over a year now that I’ve been using Ni-MH cells in these valves. The cells are slightly lower voltage than the recommended cells (1.2 versus 1.5 Volts) so do create spurious low battery warnings, but apart from that they seem to work well with adequate life before recharging. I thus anticipate continuing with their use of a means of reducing battery waste. I’ve had no cell failures to date.

Yesterday provided a good example of my HEMS in action as the electricity price dropped quite low due to stormy weather conditions. Normally at this time of year the HEMS isn’t doing much with the storage battery as daytime solar output is enough to fully charge the battery, but yesterday low pricing was enough to automatically enable both battery charging and water heating overnight. Car charging was due to run anyway driven by the demand for an hour of charging, but battery charging and water heating was triggered by the low price rather than a needed to take power for a pre-defined period of time.

HEMS schedule 9th August

The screenshot above from my phone shows the HEMS’ plan for the the early hours of the 9th. The first price column shows one hour of car charging at the cheapest price. The second column shows half an hour of water heating as the electricity price has fallen below 3.5 p/kWh when it is assumed to be cheaper than gas. The third column shows four hours of battery charging when the electricity price is below 5 p/kWh.

Metered electricity consumption (HAN side) 9th August

The above image from the HAN side of my smart meter shows the energy consumption of the house varying through the night in response to these requests from the HEMS – battery charging at the widest point, car charging above that for an hour, and water heating above that for 30 minutes.

Finally this image shows the energy consumption versus price data for the same period shows how the action of the HEMS increases electricity demand as the price drops. Indeed on this day there was virtually no consumption at any other time.

For August 9th as a whole I paid 52 pence for 7.547 kWh of electricity. Taking off the 21 pence for the standing charge leaves 31 pence for the electricity kWhs alone, an average of 4.11 p/kWh.

I recently signed up for a free home energy survey. After various questions about my home – so not much of a survey – my visitor alighted on spray foam insulation in the loft as a technology that should be of interest to me. Claims included:

Spray foam insulation would result in a better EPC rating and thus increase the resale value of my home ( “.. Eco measures are adding up to 14% on property values.. “).

Spray foam loft insulation

Given that the salesman attached some credibility to the UK’s national EPC scheme which requires an assessment of each home before sale as evidence for the buyer, then a good start point would be to see what the EPC said about my loft insulation. According to my most recent survey from September 2015 (so almost 4 years old) my home, at that time, had 100 mm of loft insulation between the floor joists with a recommendation to increase to 270 mm thickness by placing another layer of insulation across the top of the floor joists which would reduce my energy consumption by £219 over 3 years. £219 over 3 years amounts to £73 annually. In fact, since the survey was completed, I added the additional insulation recommended in October 2016 so that saving has been made and 1 point improvement on the EPC scale obtained. According to Which? magazine quoting the National Insulation Association “100mm of spray foam insulation is equivalent to around 170mm of loft insulation” so my 270 mm of conventional insulation may provide more insulation than the proposed spray foam insulation. My £73 annual saving from the EPC is far from the hundreds of pounds annually being claimed by my guest. Thus I don’t think the claimed savings are justified.

Floor level loft insulation

Then there’s the question about what the impact on my EPC rating would be. The extra 170 mm added post-2015 survey added 1 EPC point to my house rating. That’s not a big increase.

Then there’s the question about what the value of that 1 point on the EPC rating would be. According to the EPC certificate itself the indicative cost of adding 170 mm of insulation is £100 to £350 pounds. I actually paid £300. It’s not reasonable to believe that any additional value added to the home exceeds the cost of doing the work for such a small scale job. The salesman actually left a written claim that “Reports now showing that Eco measures are adding up to 14% to property prices” – I suspect that you’d need a lot of Eco measures (well beyond loft insulation) to add 14% to property prices which would be around £70,000 for my home!

Then there’s the overall question of the cost. Bearing in mind that my current insulation cost £300 and may be equally if not more effective than the spray foam then what was the spray foam quotation for? Discounted to £7,658 with marketing testimonials after the usual call to his boss to get “approval”. Which? reckons £2,500 – £3,000 for a 3-bed semi, whereas I am blessed with a substantial 4-bedroom house so it might conceivably be double the price; but for any investment on that scale I’d want to see competitive prices not just one.

Finally the question arises if I really wanted to spend £7,658 on energy efficiency would more loft insulation be best value? Our old friend the EPC has a proposal in that sort of price range, and one that it believes delivers greater savings. And that proposal is.. floor insulation for my solid concrete floors. The EPC suggests that this can save £132 annually – 81% greater savings than that extra 170 mm of loft insulation albeit at up to 20 times the price. However I already ruled out floor insulation on grounds of poor return. (My guest wasn’t persuaded as to the value of floor insulation, but a check of EPCs on similar neighbouring properties by different surveyors all identified floor insulation as a greater benefit than more loft insulation)

Recommended measures from EPC

So for me the answer is clear – I don’t see any value in spending £7,658 on alternative loft insulation. For you the answer might be different – you might be planning to convert the loft into dwelling space in which case you want insulation against the tiles/slates rather than at floor level. However if you just wanted storage space then other solutions like a shed, storage unit or skip (!) could easily prove to be better value.